Firewall

A network security device or software that acts as a barrier between your internal network (or computer) and the outside world, controlling incoming and outgoing network traffic based on predefined security rules. Think of a firewall as a bouncer or gatekeeper: it monitors connections and decides what to let in or out according to the rules you set. ‍

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For instance, a firewall might allow web browsing traffic but block unauthorized access attempts from the internet. Firewalls can be physical devices (often built into routers) or software on a computer/server.

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For a small business, the router provided by your ISP typically has a basic firewall capability - it will block unsolicited inbound traffic by default. You can also run a host-based firewall on each PC (like the Windows Defender Firewall) to control specific application traffic. Configuring firewall rules allows you to close ports that aren't needed, permit only certain IP addresses to access a service, etc.

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Firewalls are fundamental first-line defenses: they help prevent hackers from directly connecting to vulnerable services in your network and can stop certain types of malicious traffic. However, they aren't a complete solution - they work best in conjunction with other measures, and they must be configured properly (an open firewall port for remote desktop, for example, could be a risk if not managed).